Without limiting the scope of the invention, its background is described in connection with produced water generated from Oil & Gas Wells, for example frac flowback for shale gas and produced water from deepwater oil platforms. In addition, the scope of the invention also includes Exploration and Production (E&P) waste generated during the drilling of an oil or gas well or waste generated during the production of oil or gas, such as produced water, frac flowback, spent carbon, oily sludges, lime or any other E&P waste, whether solid, liquid or gas such as flare gas.
During the past decade the need for oil and natural gas has increased in dramatic fashion. With the increase in foreign oil dependency, uncertain oil prices, environmental concerns and the lack of sufficient energy supplies as seen recently in California, for example, the oil and gas industry has turned to unconventional resources such as shale gas, ultra deepwater oil in the Gulf of Mexico, oil sands, oil shale and coal bed methane.
The development of many of these unconventional fossil fuel resources requires unique approaches. For example, oil sand development is shifting from mining to in situ known as steam assisted gravity drainage (SAGD) which incorporates two horizontal wells, one placed above the other. Steam is flowed into the top injection well to “melt” the bitumen which then flows to the bottom production well. The bitumen and water flow to the surface and are separated and then the water is treated, heated and flashed to steam for reuse. Many types of waste are generated during the SAGD water treatment process.
The development of shale gas resources requires hydraulic fracturing the wells in order to stimulate the formation so that the gas can flow to the well. Since the medium used for fracturing wells is water it has now become the lifeblood of Shale plays since shale development requires significant amounts of water.
An emerging problem in the shale gas plays is “What to do with the Frac Flowback?” from shale gas wells. Shales are unconventional gas formations that are in very tight geological formations. The word tight is commonly used to mean little to no porosity. Thus, a gas shale formation does not naturally flow to the production tubing in a well.
As previously stated the well must be stimulated to flow and the most common stimulation practice today is hydraulic fracturing the well with water. The water used in hydraulic fracturing is commonly referred to as frac water. In order to get the water to flow rapidly and with as little friction as possible chemicals such as polymers are added to make the water “slick or slippery.” Now when the well has been fractured and in order to keep the fissures or fractures propped open a proppant is added to maintain a crack in the fissure for the gas to flow from the formation to the well. This is similar to keeping a crack in a door open with a door stop. The proppant is normally added to the frac water.
There are several major “WATER” problems facing the US's most attractive Shale Gas Plays such as the Barnett Shale, the Haynesville/Bossier Shale, the Antrim Shale, the Fayetteville Shale and the New Albany Shale. One is the source of the frac water. First, many residents or opposing the use of drinking water purchased by operators from municipal drinking water treatment plants. In addition, many regulators, officials and citizens are opposing the potential drawdown of the two major drinking water sources, ground water and surface water, due to a combination of recent draughts and the large volumes of water necessary for fraccing a well.
A second problem arises after the well has been fracced with water. The water and many contaminants including but not limited to metals, sand, salts, carbonates, polymers, drilling fluids, acids and various hydrocarbons return to the surface commingled and often dissolved within the water and thus is referred to as “FRAC FLOWBACK.” Gas may be produced and commingled with the frac flowback and is often flared until the well frac flowback water has ceased or reduced to the point that the well is said to be in “production.” So the frac flowback can be referred to generally as contaminated produced water.
Many engineers, geologists, well fracturing service companies and gas companies believe that there are several major reasons for using fresh water as opposed to salt water for Frac Water. First, they strongly believe that the chemical Frac Package will not blend well with salt water. Second, many geologist and petroleum engineers believe that it is necessary to partially solution mine the gas shale formation with fresh water by producing brine in order to increase porosity of the formation.
However, other engineers, geologist, gas companies and service companies believe that a gas shale formation can be fracced by partially blending a treated frac flowback with a makeup water source which may be produced water containing salts from another well or fresh water containing a low level of chlorides that is recycled wastewater. Typically, a well will flowback about 20% to 60% of the water pumped downhole. Thus, by treating the frac flowback and recycling and reusing the clean frac flowback water, then this eliminates the disposal problems associated with frac flowback.
The makeup water or remaining 40% to 80% makeup water may be obtained from municipal and industrial wastewater treatment plants. There are two major concerns with recycling treated municipal wastewater effluent. The first major concern with operators is the liability of using this water that may contain both biological and chemical contaminants. Thus, a technology may be needed to remove these contaminants to a safe level as determined by regulators and operators. The second concern may be the location of the treated wastewater effluent and the transportation logistics and costs related to either piping it to the well or using a satellite storage facility, barging the wastewater or trucking it directly to the well.
Likewise, the geographical locations of many shale plays are in close proximity to major metropolitan areas as well as valuable surface and ground water sources. Hence, Shale Gas developers are in dire need of technologies for recycling water, in particular frac flowback.
The flowback water cannot be directly reused until contaminants are reduced to a level suitable for reuse of the frac flowback as makeup frac water. In addition to high total dissolved solids (TDS) such as salts, the flowback water contains various contaminants, such as organic materials (bacteria present in the rock formation, and fracing chemicals), polymers (the friction reducers and cross-linked gels), residual hydrocarbons (trace oil, and volatile organic compounds such as benzene and toluene), and suspended solids (clay, iron oxides, and silica).
Although there are many water treatment technologies capable of removing the aforementioned contaminants, the major contaminants posing a treatment problem and preventing operators and service companies from recycling frac flowback are water based polymers such as guar and xanthane gum. The removal of these contaminants is a critical step for recycling frac flowback, whether with high TDS (salts) or flowing the fluid to a reverse osmosis system or evaporator for removal of TDS. In either case, the polymers must be removed to reduce plugging and fouling of equipment.
Many large service companies firmly believe that not only a step-change in water treatment is necessary, but a game changing technology is necessary in order to make shale gas sustainable. The current approaches in treating frac flowback and produced water via mechanical vapor recompression and reverse osmosis is neither a step-change nor game changing. These technologies are commonly employed in many other industries. Although the use of ozone produced in traditional manners, such as corona discharge, coupled with UV lamps or ultrasound to form an advanced oxidation system is a slight step-change it is not a game changing water treatment technology necessary to provide the impetus for operators to develop shale gas.
The frac flowback water treatment problem requires an out-of-the box thinking type technology that can handle virtually any type of oilfield water without plugging, fouling or the need for cleaning traditional UV lamp systems. In addition, employing corona discharge ozone generators requiring dry air or dry oxygen is another added expense.
The true impetus for sustainable gas shale would be a technology which can be used during drilling operations for treating drill cuttings, then utilized for disinfecting and treating frac water and then again used for treating frac flowback and finally when the drilling schedule is complete the same technology asset can be used for cracking methane to hydrogen and carbon or steam methane reforming to produce syngas with the goal of capturing and storing carbon (“CCS”) for enhanced oil recovery or for the production of activated carbon from nutshell, wood chips or coal as well as reactivating carbon in the field. Furthermore, the technology must be capable of operating with and coupling to existing produced water treatment systems such as gas flotation cells, nutshell filters, and activated carbon vessels.
Gas flotation is one of the most efficient and widely accepted methods used in variety of industries where removal of solid or immiscible liquid phases is of interest. In particular, in the petroleum industry, the ever-increasing volume of associated water produced from the hydrocarbon reservoirs as a side product has become a major issue to be addressed by the producers. Environmental awareness and regulations are increasingly challenging the producers to achieve a high degree of purification in the treated water streams prior to discharge or re-injection. Gas flotation has proven one of the most efficient and economical polishing processes compared to other methods and available technologies. Simultaneously, the economical penalty for additional water treatment capacity and footprint of apparatus are major factors in budgeting and decision making for the producers.
Another water treatment technology commonly found in the oilfield is activated carbon. One of the major problems with using activated carbon offshore for deepwater production platforms is that once the carbon is spent, it must be transported to shore then to a facility for reactivating the spent carbon. Likewise, gas shale frac flowback requires removal of organics but activated carbon has not been a preferred solution because of the transportation logistics involved in reactivating or disposal of the spent carbon.
The ideal plasma system for treating produced water and frac flowback on both drilling rigs and production platforms found on land and offshore would be easy to install or adapt to existing water treatment system and very robust. In addition, the plasma torch must be easy to ignite, sustain and create a dense plasma under various environments found within the oilfield. In particular, the plasma torch must not use nor require any exotic or inert gases commonly used for plasma cutting such as argon for starting the plasma torch. It must start in a complete vacuum or in a wet and flooded condition.
Texas Instruments (“TI”) teaches a method for igniting and sustaining a dense plasma in its U.S. Pat. No. 5,397,962 titled, “Source and method for generating high-density plasma with inductive power coupling” invented by Moslehi, Mehrdad M. (Dallas, Tex.) which issued on Mar. 14, 1995. Moslehi teaches, “Another important technical advantage of the present invention inheres in the fact that magnetic fields generated by the coil antenna sections can be made to rotate with respect to an axial static magnetic field, thus providing for a more uniform high-density plasmas.” Moslehi does not disclose a means for inductively coupling to an electrical arc created by an AC or DC power supply connected to carbon electrodes.
Ignition of a plasma is unreliable in a typical inductively coupled plasma reactor because it is difficult to couple to the plasma an ignition voltage high enough to excite the plasma. Specifically, very low chamber pressures, typically about 0.5 milliTorr, are necessary to achieve high plasma density in the region adjacent the semiconductor substrate and to maximize anisotropy of the sputter etch, but the voltage necessary to ignite the plasma undesirably increases with decreasing chamber pressure. Unfortunately, in an inductively coupled plasma reactor the very low chamber pressure and the lack of capacitive coupling make it very difficult to ignite a plasma in the chamber. In FIG. 1 of Moslehi's '962 patent he discloses a graph of breakdown voltage required to ignite a plasma as a function of vacuum chamber pressure for a discharge length of about 1.0 cm. This graph indicates that the optimum pressure for plasma ignition is on the order of about 500 milliTorr, and that below 400 milliTorr the breakdown voltage increases very fast as pressure is reduced. At the low pressure (i.e., 0.5 milliTorr) required for argon sputter etching, the required breakdown voltage may be close to or even exceed the capacity of the RF power source of the induction coil, making plasma ignition unreliable. As a result, it may be necessary to make several attempts to ignite a plasma, greatly reducing the productivity of the plasma reactor.
FIG. 2 of the '962 patent illustrates an inductively coupled plasma reactor of the prior art useful for argon plasma sputter etch processing having a cylindrical induction coil 10 around a cylindrical quartz reactor chamber 20 and lid 30, one end 10a of the coil being connected to an RF source 40 through a suitable RF matching network and the other end 10b being grounded. Plasma ignition relies upon the electrical potential between the “hot” end 10a of the coil 10 and the nearest grounded conductor in the chamber, such as the wafer pedestal 35. Thus, the discharge length is the distance between the hot coil end 10a and the nearest surface of the wafer pedestal 35.
A conventional technique for meeting the power requirement for plasma ignition is to connect an auxiliary RF power source to the induction coil during plasma ignition, but this requires additional hardware and expense.
Another conventional technique is to temporarily raise the chamber pressure when igniting the plasma and then, after the plasma is ignited, quickly reduce the chamber pressure to the desired processing pressure. However, pumping down the chamber pressure after plasma ignition (e.g., from 10 milliTorr during ignition to 0.5 milliTorr after ignition) requires a significant amount of time, during which the etch process will be carried out at a higher than ideal pressure, thereby causing poor etch profiles. Also, the necessary time to pump down will adversely affect throughput of the etch reactor.
Yet another conventional approach is to temporarily increase capacitive coupling during ignition by applying RF power to the wafer pedestal. However, this tends to create a large spike in the D.C. bias on the wafer during plasma ignition, increasing the risk of wafer damage.
U.S. Pat. No. 4,918,031 discloses how to introduce a so-called Faraday shield between the entire induction coil 10 and the plasma in the reactor of FIG. 2 (discussed above) and apply a separate electrical power source to the Faraday shield in order to control the electrical potential of the plasma or to ground the Faraday shield in order to suppress capacitive coupling by shielding the plasma from electric fields. A disadvantage of this technique is that it either unduly increases capacitive coupling to the plasma if used to increase the plasma potential, thereby reducing the control over ion energy, or else, if grounded, it cuts off whatever capacitive coupling from the induction coil may exist, thereby making plasma ignition less reliable or more difficult.
U.S. Pat. No. RE29304, “Plasma light source for spectroscopic investigation” issued to Greenfield et. al on Jul. 12, 1977 discloses a means for plasma ignition by inserting a carbon rod into a RF field. For example column 5, lines 15 to 50 disclose “A carbon rod is introduced into the open end of the vessel 1 as far as the jet 9. The rod is heated by high frequency currents produced therein and heats the surrounding gas which is thus ionised sufficiently to initiate a stable plasma which forms an annulus owing to the “skin effect.” The rod is withdrawn and the plasma is now maintained by the operation of high frequency eddy currents and capacitively induced currents resulting from the flow of current in the coil. Argon gas is fed into the injector inlet 8 at a rate of five liters per minute. The powder sample is placed in the drum 11, which is rotated by the motor 13 at a rate of about 500 r.p.m. The powder is drawn up the capillary tube 10 and sprayed through the low temperature central region of the plasma to form a tail flame at the open end of the tubular vessel 1. The spectrum of this flame may be analyzed using a suitable spectrometer.
The production of the plasma in annular form instead of a plasma ball and the directing of the substance along the axis of the plasma annulus provides a convenient way of bringing the substance into the tail flame region. The use of the tail flame of the plasma to burn the substance is advantageous in that the plasma temperature is frequently higher than is desirable for analysis and in that the temperature of the tail flame can be adjusted by varying the voltage applied across the coil. This flexibility is desirable in view of the fact that the optimum temperature for analysis varies from substance to substance, and the temperature variation is much greater than can be obtained with conventional flame sources, for example air/acetylene burners, and whilst D.C. or A.C. are systems will give higher temperatures than such burners they also produce sample contamination.”
Greenfield et. al RE29304 specifically discloses removing the carbon rod in order to not contaminate a sample. He does not disclose nor is it obvious to leave the carbon rod within the torch and continuously feeding the carbon rod as a source of fuel. Nor does the patent disclose a second carbon electrode. Likewise, there is no disclosure nor mention of coupling the carbon rod to a DC power supply in order to form an arc for creating, sustaining and forming a dense plasma.
U.S. Pat. No. 6,291,938, issued to Jewitt et. al and published on Sep. 18, 2001 titled, “Methods and apparatus for igniting and sustaining inductively coupled plasma” relates to improved methods and apparatus for igniting and sustaining inductively coupled plasmas produced from radio frequency (RF) power for process operations.
Jewitt's '938 patent describes the problem inherit with RF ICP torches related to igniting and sustaining the plasma. It states, “RF plasma is extensively used in a wide variety of applications for carrying out process operations. For example, thermal plasmas can be used to promote chemical reactions because of the high temperatures of the thermal plasma. Alternatively, thermal plasmas are able to promote chemical reactions because of the ability of the energetic electrons to break chemical bonds and allow chemical reactions to occur that would proceed with difficulty under non-plasma conditions.
In other applications, RF power is used to produce non-thermal plasmas, also referred to as non-equilibrium plasmas. The manufacture of semiconductor devices is one area in which non-thermal plasmas are extensively used. During the manufacture of semiconductor devices, etch processes involving RF plasmas and deposition processes involving RF plasmas are used repeatedly during the fabrication process. One of the main benefits of using the non-thermal plasma is the ability of the non-thermal plasma to stimulate chemical reactions that would otherwise require temperatures that are too high for use in the fabrication of semiconductor devices.
RF non-thermal plasmas are also used in cleaning processes in manufacture of semiconductor devices. The non-thermal plasmas are commonly used to strip photoresist materials from semiconductor wafers as part of post etch wafer clean procedures. Resist material is stripped from the surface of the wafers by creating a non-thermal plasma in a gas containing oxidizing species such as oxygen and possibly halogen species that are capable of reacting with and volatilizing the resist material. In some applications, the non-thermal plasma is maintained at a position upstream of the wafer. Reactive species generated in the non-thermal plasma flow downstream and react with the wafer surface for the stripping process. Another cleaning process that uses non-thermal plasmas is the cleaning of reaction chambers used in semiconductor manufacturing.
RF plasmas have also been used for decomposition of chemical compounds that are hazardous or otherwise undesirable. Some of the compounds are highly refractory in nature and are difficult to decompose. Examples of compounds that have been decomposed or abated with plasmas include chlorofluorocarbons (CFC) and perfluorocompounds (PFC).
One frequently encountered problem with standard inductively coupled RF plasma systems is the difficulty of igniting and sustaining the plasma. Plasma ignition is unreliable because coupling an ignition voltage high enough to generate the energetic species needed to produce the plasma is difficult. The voltage required to generate the energetic species is frequently referred to as the breakdown voltage. The breakdown voltage for a gas depends upon a variety of factors. Two major factors are the pressure of the gas and the electronic properties of the gas such as the electronegativity of the gas and its plasma products. The absolute value of the magnitude of the breakdown voltage undergoes a minimum with respect to the pressure of the gas. Specifically, the magnitude of the breakdown voltage increases for plasma ignition at pressures higher or lower than the pressures at which the minimum breakdown voltage occurs. Consequently, igniting plasmas at very low pressures and at high pressures is difficult. The electronegativity of the gas affects the magnitude of the breakdown voltage so that the gas with higher electronegativity requires higher breakdown voltages at every pressure.
Unfortunately for standard inductively coupled plasma technology, the absence of strong electric fields and the absence of strong capacitive coupling make it difficult to overcome the plasma ignition problems resulting from gas pressure and gas electronegativity. At pressures that are too high or too low or for gases with high electronegativities, the required breakdown voltage may equal or exceed the capacity of the RF power source, making plasma ignition unreliable. As a result, it may be necessary to make several attempts to ignite the plasma, greatly reducing the productivity and efficiency of the plasma process. The unreliable plasma ignition can waste valuable process gases, can increase pollution problems, and can ruin valuable product
In addition to the problem of igniting the plasma, there is also the problem of poor plasma stability. After the plasma has been ignited it is possible for the plasma to go out, i.e. become extinguished, because of changes in RF power delivery conditions. For instance, the plasma can go out while performing a process and cause the same unfortunate results that occur for unreliable plasma ignition.
Clearly, there are numerous applications requiring reliable and efficient methods and apparatus for igniting and sustaining inductively coupled RF plasmas. Unfortunately, typical methods and apparatus for old-style inductively coupled RF plasma systems have characteristics that are undesirable for some applications.
Without limiting the scope of the invention, its background is also described in connection with tangentially fired boilers. The U.S. Department of Energy's (“DOE”) National Energy Technology Laboratory (NETL) has stated, “Since T-fired boilers make up 44 percent of the world's installed base and 41 percent of that of the United States, a technology solution for T-fired boilers is important to address both existing and new units . . . . Oxy-combustion is a promising, near-term technology for carbon capture from pulverized coal (PC) fired power plants. Oxy-combustion replaces combustion air with a mixture of oxygen and recycled flue gas, creating a high carbon dioxide (CO2) content flue gas stream that can be more easily processed for sequestration or high purity product. For more than a decade, Alstom Power, Inc. and others have been actively working on various oxy-combustion-based CO2 control technologies. In these projects, a large body of scientific information and knowledge has been accumulated, but product development and technology gaps exist. In particular, oxy-combustion characteristics in a tangentially fired (T-fired) boiler are not well understood. Furnace aerodynamics and mixing with T-firing is vastly different from swirl-stabilized, wall-fired burners that require different design considerations to optimize oxy-combustion.”
Likewise, the DOE has defined Innovative Confinement Concepts as a broad-based, long-range research activity that specifically addresses approaches that could lead to the attractive and practical use of fusion power. Likewise, there are many other reasons for confining plasmas. Current plasma confinement uses range from as simple as plasma cutting torches to increasing the life of ordinary household lamps and light bulbs to waste processing. One of the reasons for confining a plasma is to protect the plasma facing material (PFM)—the vessel. Modern day plasma torches can produce plasma gas temperatures as high as 50,000° F. There is no material known to science that will remain a solid at plasma temperatures of 50,000° F. In fact, carbon has the highest known melting point of all solids. Thus, in order to use known materials as plasma facing components the plasma must be confined in such a manner that the PFM survives while retaining its shape and structural strength for a specified time period. However, as the DOE has noted confining plasma is the Holy Grail to fusion power. Plasma can be confined by several means. The two practical approaches are inertial confinement and magnetic confinement. Magnetic confinement couples a magnetic field to the plasma in order to confine it. On the other hand, inertial confinement uses the inertia of a rotating fluid in many cases the plasma itself to confine the plasma and keep it away from the walls of the vessel it is confined within. Hence, an inertia confined rotating plasma will obey the laws of conservation of angular momentum.
The true impetus for sustainable heavy oil, oil shale or oil sand production, carbon capture and CO2 enhanced oil recovery would be a technology which can take the bottom of a barrel, petroleum coke produced from cokers in refineries and convert it at the wellhead into useable products. For example, a compact and portable technology which can convert coke into CO2 or syngas (CO+hydrogen) or (CO2+Hydrogen), then separate the CO2 from the hydrogen for injecting the CO2 downhole for EOR purposes while using the hydrogen at the wellhead for upgrading heavy oil, while treating associated gases and water produced with the heavy oil would solve many upstream problems as well as downstream refinery problems.
The CO2 enhanced oil recovery (EOR) problem requires an out-of-the box thinking type technology that can be deployed in virtually any type of upstream O&G operation such as deepwater offshore production platforms, SAGD oil sand production facilities or environmentally sensitive areas such as Alaska. The current approach in upgrading oil sand bitumen via large and expensive cokers is neither a step-change nor game changing. In fact, the cost of currently designed upgraders has put many projects on hold due to low crude oil prices.
Without any doubt plasma could change those problems associated with production and treatment of oilfield waste, upgrading heavy oil, bitumen, kerogen, flaring associated gas and treating produced water from oil and gas wells. Likewise, plasma could be the one single impetus for sustainable coal fired plants with respect to emerging green house gas emission problems.
However, there have been five major drawbacks and/or concerns in using plasma for industrial applications such as gasifying, cracking or steam reforming coal, petcoke, heavy oil, oil sand, oil shale, cracking methane and/or converting biomass to biochar. The drawbacks are electrode life, heat rejection, plasma ignition, sustaining a plasma and plasma confinement. Without a doubt the number one problem that must be solved in using plasma for the aforementioned applications is confinement due to the extreme temperatures the plasma facing material or refractory must survive in order to bridge the gap between R&D and commercialization. Shutting down a reactor every other month for a turn around in order to reline the reactor or repair the refractory is not an option in many applications. Many plants must operate their reactors continuous duty between turnarounds which may be upwards of two years.
In addition, the second and third major drawbacks—electrode life and heat rejection—must be solved in order to make plasma a sustainable and widely accepted technology. Most plasma torches reject upwards of 30% of the rated torch power as heat into its cooling water. This is due primarily to heat loss due to cooling the electrodes. The electrodes are cooled in order to prolong the life of the electrode. In light of this there is not a single industrial application worldwide where a plasma torch has been operated 24/7 for more than a few thousand hours which equates to shutting down the torch to replace electrodes every other month. In addition, once the plasma is ignited it must be sustained similar to keeping the fire lit in any boiler, furnace, thermal oxidizer or engine. This has been a major issue with using inductively coupled plasma (ICP) torches. Thus, many large scale applications have utilized DC or AC electrode type plasma torches. Once again, the benefits of using an electrodeless torch, not having to worry about electrode life, are outweighed by the inability to sustain a plasma with an electrodeless ICP torch.
As a result, there is a need for a simple plasma torch design that uses consumable electrodes while recuperating the heat generated from the torch. Likewise, many energy companies, such as coal utilities and oil companies, believe that not only a step-change in plasma torches and their inherit capital and operating costs are necessary, but a game changing plasma reactor design is necessary in order to make plasma gasification a reality and sustainable. Likewise, the DOE and Universities are in dire need of a simple plasma reactor design for conducting plasma R&D such as confinement, rotation and testing plasma facing material.
In light of the above references, there exists need for a cost-effective apparatus for studying rotating plasmas as well as confining a plasma that can be used at the DOE and academia level as well at laboratories owned and operated by Industry ranging from Oil and Gas companies, Petrochem Companies, Chemical Companies, Pharmaceutical Companies, Utilities and other such companies that conduct research. In addition, with rising energy oil prices, global warming, and greenhouse gas emissions there exists a need for industrial application of a relative inexpensive plasma rotation method, system or apparatus that can be used to modify existing equipment, such as a tangentially fired boiler, honeycomb base (HCB) tank, column, fluidized bed combustor, or gasifier by means of one or more plasma modules.